This study is concerned with investigating experimentally the effects of methanol blending to base gasoline on the performance and fuel cost of a spark ignition (SI) engine. The fuel blends were prepared by blending 5, 10, 15, and 20 vol % of methanol with a specified amount of base gasoline. These fuel blends were designated as M5, M10, M15, and M20, respectively. Base, leaded, and unleaded gasolines were also used in the study. The experiments were conducted under various engine speeds, spark timings (STs), and compression ratios (CRs). The engine was operated under wide-open-throttle (WOT) conditions. The result of the study showed that the M5 blend yields the best engine performance in terms of the brake mean effective pressure (bmep), while the M20 blend suggests the best performance in terms of brake thermal efficiency (bte). The economical analysis performed in the study is based on both the current blending fuel prices in Turkey and brake-specific fuel consumption (bsfc) of the engine while using base gasoline and gasoline-methanol blends. It was obtained that, in contrast to the improvement of engine performance, methanol blending caused an increase in the consumed fuel cost because of the expensive methanol price in Turkey. The increments in the cost of the fuel blends compared to base gasoline were determined as 18.86, 36.95, 54.20, and 73.01 % for M5, M10, M15, and M20, respectively. Uncertainty analysis was also performed in this study, and it was found that the uncertainties in the measurement devices do not have noticeable influences on the variations of engine characteristics.